The broad objective of the proposed research is to develop, implement, and evaluate accurate and efficient approaches to image reconstruction in single- and multi-slice helical computed tomography (CT). The numerous advantages of helical CT, such as its high volume-scanning speed, have allowed it to displace conventional CT as the test of choice in many clinical situations and allowed for the development of new imaging protocols that were not even possible with conventional CT. The investigators' preliminary theoretical and empirical studies strongly suggest that the proposed reconstruction approaches preserve all of the inherent advantages of helical CT available when existing reconstruction approaches are used while improving physical characteristics such as aliasing response, longitudinal resolution, and noise properties, with little or no additional computation burden. Such improvements have a number of clinical implications: (a) Improved longitudinal resolution can enhance the diagnostic accuracy of focal pathologic abnormalities such as lung nodules. (b) The ability of the approaches to reduce or control image noise levels in optimal ways can be exploited either for improving image quality for a given patient radiation exposure or for reducing patient exposure while holding image quality constant. Reduced exposure also reduces the burden on overworked x-ray tubes. (c) The approaches can yield reconstructed volumes that have more isotropic noise and resolution properties than can existing approaches, which would improve the quality of multiplanar reformats generated form these volumes. (d) Most significantly, the proposed approaches would allow clinicians to trade off the resolution and noise improvements for improved temporal resolution. This would particularly benefit CT angiography, where improved temporal resolution translates directly into improved bolus tracking and thus improved image contrast. The specific aims of the proposal are: (1) development of a Fourier-based longitudinal interpolation approach for helical CT; (2) development of a spline-based longitudinal interpolation approach for helical CT; (3) development of optimal methods for the exploitation of redundant fan-beam information; (4) development and evaluation of novel fan-beam reconstruction algorithms; and (5) evaluation of the physical characteristics and clinical-task performance of all of the proposed approaches; with comparison to existing approaches.